1. Field of the Invention
The present invention relates to rotation-angle detecting devices, and more particularly, to a low-profile and compact rotation-angle detecting device having a simple configuration.
2. Description of the Related Art
A known type of rotation-angle detecting device will be described with reference to FIGS. 7 and 8. FIG. 7 is a plan view showing the inner configuration of the rotation-angle detecting device, and FIG. 8 is an explanatory view showing the output characteristics of the rotation-angle detecting device with respect to the rotation angle.
Referring to FIG. 7, a rotating member 23 is mounted inside a case body 22 made of insulating resin. The rotating member 23 is made of insulating resin, is shaped like a cylinder, and is rotatably supported by the case 22. A shaft of a steering wheel of an automobile extends through the rotating member 23 so that the rotating member 23 is rotated clockwise and counterclockwise together with the steering wheel. A helical gear 23a having a plurality of teeth is formed on the entire outer peripheral surface of the rotating member 23.
A rotation shaft 29 is rotatably provided inside the case body 22. A driving gear 28 is fixed to the rotation shaft 29. A helical gear 28a having a plurality of teeth is formed on the entire outer peripheral surface of the driving gear 28, and is meshed with the helical gear 23a of the rotating member 23. A first ring-shaped magnet 25A having a pair of magnetic poles on its outer peripheral surface is provided adjacent to the driving gear 28 so that it is coaxial with the rotation shaft 29. The rotation shaft 29 is made of metal such as brass or aluminum, and has a spiral screw groove 29a formed from the center to one end. A moving member 24 is engaged with the screw groove 29a. 
The moving member 24 has a through hole extending from one end face to the other end face in the moving direction. The through hole has, on its inner peripheral surface, an internal thread (not shown) to be meshed with the screw grove 29a formed on the rotation shaft 29. A second magnet 25B having a pair of magnetic poles is fixedly attached to the lower surface of the moving member 24. The moving member 24 is guided inside the case body 22 so as to linearly move in the axial direction of the rotation shaft 29. When the rotating member 23 rotates and the driving gear 28 and the rotation shaft 29 also rotate, the moving member 24 and the second magnet 25B reciprocally move in the axial direction of the rotation shaft 29.
A substrate 30 on which first and second Hall elements (detection means) 26A and 26B are mounted is fixed in the lower part of the case body 22. A pair of first Hall elements 26A face the first magnet 25A, and the second Hall element 26B faces the second magnet 25B. When the rotation shaft 29 rotates, the first Hall elements 26A detect the magnetic displacement of the first magnet 25A, and output predetermined sinusoidal waves 101 and 102 shown in FIG. 8 as first detection signals in response to the rotation. When the second magnet 25B is reciprocally moved in the axial direction of the rotation shaft 29 along the screw groove 29a, the second Hall element 26B detects the magnetic displacement of the second magnet 25B, and outputs a signal 103, which linearly changes over the entire rotation angle range of the steering wheel, as a second detection signal. The absolute angle of the rotation angle (steering angle) of the steering wheel can be detected on the basis of the first and second detection signals output from the first and second Hall elements 26A and 26B.
In the above-described known rotation-angle detecting device, however, a driving gear with a helical gear to be meshed with the helical gear on the outer peripheral surface of the rotating member must be provided, and the driving gear and the rotating member are arranged so that their rotation axes are orthogonal to each other. Consequently, the thickness and size of the rotation-axis detecting device are increased by of the diameter of the driving gear.
Accordingly, it is an object of the present invention to provide a low-profile compact rotation-angle detecting device that can measure the absolute angle with a simple configuration.
In order to achieve the above object, according to an aspect, the present invention provides a rotation-angle detecting device including a rotor, a first output mechanism for outputting a first detection signal in response to the rotation of the rotor, and a second output mechanism for outputting a second detection signal in response to the rotation of the rotor, wherein a first transmission gear and a second transmission gear having intermittent teeth are arranged along the rotation axis on an outer peripheral surface of the rotor, the first output mechanism includes a first output gear that is meshed with the first transmission gear and that rotates on an axis in parallel with the axis of the rotor, and a first output section for outputting the first detection signal in response to the rotation of the first output gear, the second output mechanism includes a second output gear that is meshed with the second transmission gear and that rotates on an axis in parallel with the axis of the rotor, and a second output section for outputting the second detection signal in response to the rotation of the second output gear, and the rotation angle of the rotor is detected as an absolute angle on the basis of the first detection signal and the second detection signal.
The above features make it possible to provide a low-profile compact rotation-angle detecting device that can measure the absolute angle with a simple configuration.
Preferably, the first detection signal has a predetermined period and continues within the rotation range of the rotor, and the second detection signal rises or falls stepwise within the rotation range of the rotor.
This allows the rotation-angle detection device to measure the absolute angle with high precision.
Preferably, the second output gear includes upper and lower tooth segments arranged vertically and alternately, the upper tooth segment is meshed with the second transmission gear, and the lower tooth segment engages with the outer peripheral surface of the rotor after the upper tooth segment is rotated by a predetermined angle in engagement with the second transmission gear, thereby preventing the second output gear from returning.
In this case, the second output gear can be prevented from returning with a simple structure, and the accuracy in detecting the rotation angle can be increased.
Preferably, each of the first output section and the second output section includes a permanent magnet with different magnetic poles opposing each other with the rotation axis therebetween, and a magnetoresistive element whose resistance varies depending on the direction of a magnetic field of the permanent magnet.
In this case, the rotation angle can be detected in a non-contact manner. Moreover, since the magnetoresistive element is used, the detection accuracy can be increased, regardless of assembly accuracy.
Preferably, the first output mechanism is a non-contact magnetic output means, and the second output mechanism is a contact output means.
In this case, since the second output mechanism is less expensive than the first output mechanism, the cost can be reduced. Moreover, since the number of revolutions of the second output mechanism is smaller than that of the first output mechanism, the second output mechanism can stand long use.
Preferably, the second output mechanism is a rotary variable resistor.
Since the second output mechanism can be thereby made even less expensive, the rotation-angle detecting device can be provided at a lower price.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.